488 BIOLOGY. 



3007. The osseous and muscular system first makes 

 its appearance, when the vegetative parts are present. 



3008. The intestines, the vessels, and the commence- 

 ment of the sexual parts are originally situated in the 

 umbilical cord, which is itself surrounded by the integu- 

 ment. The umbilical cord is therefore nothing else than 

 the posterior extremity of the body or abdomen, through 

 which the embryo respires and is nourished. 



3009. The first respiration and deglutition is there- 

 fore a respiration and deglutition effected by the sexual 

 parts, as in the lowest animals. 



-^-'tr-vt/H* fa- 



^ ' / 

 b. Functions of the Fcetus. 



1. Nutrition. 



3010. The juices which are contained in the develop- 

 mental sacs are nutritive juices or chyle ; they contain 

 principally albumen. The chyle of the intestinal vesicle 

 depends upon the vitellus. 



3011. The foetal water in the amnion is derived from 

 albumen in the ovum ; it is here secreted by the oviduct, 

 but in the Mammalia by the internal wall of the uterus, 

 and absorbed by the general envelopes. 



3012. The cause of this secretion resides in the de- 

 composition of the blood through the influence of the 

 chorion. Thus if the maternal blood become deoxydized, 

 it must necessarily revert to the condition of chyle. This 

 chyle is the foetal water. 



3013. The foetal water is absorbed by the embryo 

 through the integument. 



3014. No blood is transferred from the mother directly 

 to the foetus. 



3015. The blood-vessels of the uterus and placenta do 

 not open into or communicate with each other. 



3016. The foetal water corresponds to the albumen or 

 the white of eggs, not to the vitellus. This becomes 

 also during incubation consumed in the formation of the 

 body of the chick, and not the vitelline mass, which is 

 first of all destined for the intestine. 



